The goal of this proposal is to understand the mechanism by which Hunk acts intracellularly and determine the role of Hunk protein in tumorigenesis. The first aim of this proposal will address the participation of Hunk in Neu-driven mammary tumorigenesis. These experiments are important to determine the mechanisms by which Neu acts on tumor formation and maintenance. As Neu abberrations are observed in ~30% of human breast cancers, these studies will provide additional insight into the development of more effective treatments. This aim will be addressed using in vivo genetic approaches that employ a mouse model that encorporates an inducible system to drive Neu oncogenesis. These animals will then be crossed with Hunk deficient mice to generate Neu-inducible Hunk wildtype and deficient animals. These animals will be used for long-term chronic induction studies to identify a role for Hunk in tumor latency and multiplicity. In addition, short-term inductions will be performed to characterize the affect of Hunk on Neu-driven cell growth and proliferation. Finally this system will be used to address the role of Hunk in Neu-specific signaling. The second aim of this proposal will address the role of Hunk in PI3K-Akt signaling. As Hunk is a recently discovered protein kinase, little is known about its role as a signaling molecule. However, we have obtained preliminary evidence implicating Hunk in PI3K-Akt signaling. To address the second aim we will employ cell biology and biochemical techniques to establish the relationship between Hunk and PI3K-Akt signaling in the mammary gland. Specifically, we will determine whether a physical interaction exists between Hunk and Akt, whether Hunk is a substrate of Akt, and whether the activation of Akt through PI3K impinges on Hunk protein levels and/or activity. Experiments will also be performed to address the whether Hunk activity and/or levels affect the signaling capacity of Akt through PI3K. Finally, these experiments will include in vivo genetic studies to determine whether Hunk influences Akt-dependent tumorigenesis. The Akt pathway is mutated in many human cancers and, similar to Neu, there is frequently an increase in Akt activity in breast cancers. Consequently, the studies outlined in this proposal are important for understanding the molecular basis of breast cancer and how it can be more effectively treated. It is estimated that breast cancer will be the leading cause of cancer-related death in women in 2006. Several protein kinase inhibitors have been extremely effective for the treatment of human cancer. As such, characterization of novel therapeutic targets is an important element for improving human health.